The foremost step is to open OST Recovery software. After opening this, follow this simple step:Go to Start > Programs > OST Recovery software > easily Convert OST to PST File.
Now, Add OST files to convert it into PST file format.
Your OST files will be loaded and its contents will be visible as shown in below screenshot.
Last important step is to select the folders (present in the left pane on the Window) in order to save them. Towards the bottom of the Window, select 'Save' button. You will see that software will start saving process as seen in below snapshot:-